Other ID: ATL2 89-4; 89, Leg 4
Organization(s): USGS, Woods Hole Coastal and Marine Science Center
Location: Baltimore Canyon Trough area, outer continental shelf, United States, North America, North Atlantic;
Principal Investigator(s): Harley J. Knebel
Information Specialist(s): Nancy K. Soderberg
Data Type(s): Location-Elevation: Navigation, Sampling: Biology, Sampling: Geology, Seismics: Sparker, Seismics: Sub Bottom Profiler
Scientific Purpose/Goals: This 4th leg of the ATLANTIS II cruise had 3 primary objectives. The first objective was to obtain long vibracores to deduce characteristics and ages of sub-bottom sediments. These cores were in support of the acoustic survey completed in Baltimore Canyon Trough in May 1974. Second, short cores of sub-bottom sediments were to be collected. By measuring relative amounts of Pb-210 in these short cores, ages and accumulation rates of sediments for the past 100 years could be determined. Finally, stability of sediments at shelf edge was to be studied. Near-surface (apparently recent) fault displacement had been observed in high-resolution seismic records, suggesting that a mechanism existed for generation of slumps at the shelf break and on the upper continental slope. In addition, several special studies were pursued: sampling surface sediments to determine trace metal and hydrocarbon contents; sampling suspended sediments at water surface; emplacement of pipes into the sea floor by vibracore rig to use as reference points during submersible dives; outlining the areal extent of a sand-wave field near Wilmington Submarine Canyon; dropping sea-bed drifters at selected sites; and outlining the path of the ancestral Delaware valley across the continental shelf.
Start Date: 1975-06-01
Start Port/Location: Woods Hole, MA
End Date: 1975-06-12
End Port/Location: Woods Hole, MA
Equipment Used: 3.5 kHz, Alpine Vibracorer, Raytheon 3.5 kHz sonar (CESP II) system, Del Norte 26 sparker, Corer - piston, Smith-MacIntyre grab, Corer - gravity, Sediment traps, Magnavox satellite positioning system, Loran-C, Seismic Engineering streamer
Information to be Derived:
Summary of Activity and Data Gathered: Cruise concentrated on vibracoring and bottom sampling off New Jersey. 3.5 kHz records: 1774 km; Minisparker records: 659 km; Sample stations: 42; Bottom sediment samples: 78 (Vibracores: 19; Hydrostatically damped gravity cores: 37; Smith-McIntyre grab samples: 15; Gravity cores: 7); Suspended sediment samples: 50; Sea-bed drifters released: 57; Reference pipes emplaced in sea floor: 3.
Staff: Michael Bothner, Patricia Forrestel, Raymond E. Hall, William Jaworski, Frank W. Jennings, Harley J. Knebel, Francis A. Kohout, Charles Meeder, David Twichell
Notes: The 3.5 kHz system did not work properly during the bulk of the cruise; only a bottom trace could be obtained on the continental shelf and the signal usually was lost on the continental slope. It functioned as a fathometer during most of the cruise. The vibracore operations were hampered for several days by weather and sea state. Also (sometimes unpredictably), ship drift while anchored caused delays in time at station and retrieval of vibracore air hose. (The air hose fouled 3 times around the ship's rudder.) Thirdly, water-depth limitation caused the air hoses on the rig to collapse several times; maximum water depth for successful coring was 80 m. Also anchor deployment and weighing took more time than anticipated. Anchoring delays cut into total vibracoring time. Original Center People field also contained: Bob Carson - watch chief (Lehigh U./USGS).